The invention relates to blow molding processes and to apparatus for making blow-molded articles.
Conventional blow-molded containers generally have small-diameter top ends that are threaded to accept screw-on caps. In some applications, such top ends are undesirable because of the nature of the contents of the container, which in some cases may require wide-mouth openings to facilitate getting the contents into and out of the container. Thus, alternative closures such as seal-on membranes or seamed-on metal closures would be desirable in many cases.
However, it has not been practical or cost-effective to employ seal-on membranes or seamed-on metal end closures for such containers because the blow-molding process has not allowed for easily making the type of flat, outwardly extending flanges required for such closures. To provide such a flange in a blow-molded container, it has been necessary to form an intermediate blow-molded article in a particular manner and then perform finishing operations on the intermediate article. More specifically, the tubular side wall of the intermediate article is molded to include a hollow generally U-shaped section that extends radially outwardly from the side wall. A lower leg of the U-shaped section extends generally radially and will form the flange on a finished container. The lower leg is joined at its outer end to the rest of the generally U-shaped section. After removing the intermediate article from the mold, the article is subjected to two separate cutting operations. In a first cutting operation, a cut is made near the outer edge of the lower leg of the U-shaped section to sever the leg from the rest of the section. A second trimming operation is then performed by cutting through the lower leg in the axial direction to remove a radially outer end portion of the leg. The remaining portion of the leg thus forms a flange on the container. This post-mold finishing process is relatively complicated and costly. It would be desirable to provide a flanged container in a simpler and less costly manner.
It has also been suggested, for instance in U.S. Pat. No. 4,496,064, that a high degree of biaxial orientation in the flange of a plastic container is needed to tolerate high bending stresses placed on the flange when a metal closure is double-seamed onto the container. The '064 patent teaches a stretch blow molding and finishing process to achieve such high degree of biaxial orientation. In particular, an intermediate article is stretch blow molded and post-mold finishing operations are performed as previously described to produce the finished container, such that the flange is formed from a portion of the intermediate article subjected to biaxial stretching. As noted, the post-mold finishing operations are relatively costly. Furthermore, with the conventional stretch blow-molding process, the flange thickness is constrained to be uniform in the radial direction and essentially equal to the thickness of the side wall of the container. It would be desirable to be able to vary the flange thickness and/or profile as required in each instance.
In co-pending application Ser. No. 10/224,101, an improved process is disclosed for forming a blow-molded container, in which a solid radially outwardly extending flange is blown into the tubular side wall of the article. A circumferentially extending recess or groove is formed in the inner surface of the mold that molds the tubular side wall of the article. A parison of thermoplastic material is extruded from an annular throat of a die, and the parison is enclosed in the mold. While the thermoplastic material is still flowable, the parison is inflated by blowing to blow the thermoplastic material against the walls of the mold. During the inflation, the groove is filled by the flowable thermoplastic material. The material cools and solidifies and the resulting article is removed from the mold. The material that filled the groove forms a solid radially outwardly extending flange molded to the tubular side wall of the article.
This process is an improvement over prior processes as noted above, in that the complexity of post-mold finishing operations is reduced and the flange thickness can be controlled independently of the container wall thickness by suitably configuring the groove in the mold wall. It has been found, however, that it can be difficult to completely fill the groove when the radial length of the groove is relatively large in comparison with the axial width of the groove (i.e., when the flange is long and thin).